An in-vehicle apparatus such as a navigation apparatus displays a map of the vicinity of a present position on a display screen based on map data, and calculates an optimum route to a destination to thereby navigate the vehicle or driver. A storage medium to store the map data uses a hard disk drive. The hard disk drive, which has a large data volume, further stores music data, application software for operating the navigation apparatus, and image or audio data used in an audio function integrated into the navigation apparatus, in addition to the map data.
The hard disk drive is a storage medium where data are written and read with a magnetic head on a disk to which magnetic materials are applied. During the operation of the hard disk drive, the disk rotating at a high speed rotates an ambient air to generate a pressure. The magnetic head thereby marginally floats above the disk. If the hard disk drive operates under the environment where surrounding atmospheric pressure falls remarkably, the air pressure floating the magnetic head is decreased and the gap between the disk and magnetic head cannot be maintained in the proper state. As a result, the magnetic head may collide with the disk to thereby damage it. Since an atmospheric air pressure falls as an altitude rises, the hard disk drive has an application limit in altitude. Generally, the operation guarantee relative to the altitude for the hard disk drive is up to an altitude of 3000 m (about 0.7 atmosphere) to 5000 m (about 0.5 atmosphere).
The countermeasure for preventing damage of the hard disk drive mounted in the in-vehicle apparatus is thereby needed when used at a high upland (e.g., higher than 3000, 4000, or 5000 meters high) exceeding the guaranteed altitude where the operation of the hard disk drive is guaranteed.
Patent document 1 describes the following technology. When the relevant vehicle ascends up to a predetermined altitude (for example, 3000 m), some map data stored in the hard disk drive are copied or stored also into an external memory. The hard disk drive is then stopped; navigating is performed based on the map data stored in the external memory during the travel in the high upland area at an altitude not lower than 3000 m. Thus, such technology stops or disables the hard disk drive at a high upland area to thereby prevent the damage of the hard disk drive while allowing navigating.
Data is previously prepared for a method of a high upland area determination as to whether a relevant position is in a high upland area. A present position of a vehicle is referred to the prepared data so that the high upland area determination can be executed for the present position.
In such a method, for example, a region on a map or a map coordinate plane is divided into divisions every predetermined interval relative to latitude and longitude. Each division is assigned with high upland information indicating whether to include a high upland having an altitude equal to or greater than a predetermined altitude. Data for determining a high upland area (referred to as high upland area determination data) is prepared by including divisions assigned with the high upland information. A present position of a vehicle is thus referred to the high upland area determination data so that whether the present position is in a high upland area.
Since a hard disk drive may stop in a high upland area, it is necessary to perform high upland area determination based on the high upland area determination data even if the hard disk drive is stopping. For such necessity, it is important to previously store the high upland area determination data in a storage device other than the hard disk drive. Storing high upland area determination data corresponding to the whole of a map covering a country, a continent, or a global region needs to prepare a remarkably large data volume. In addition, when the data volume increases by updating the high upland area determination data, there is also a disadvantage that the storage capacity needs to be increased accordingly.                Patent document 1: JP-2004-317385 A        